Abstract
The identification of a number of cis-elements which direct gene expression in maize endosperm, and the characterization of corresponding DNA binding proteins, point to the interaction of different classes of transcription factors in this tissue. To assess whether MADS box genes are also involved in maize endosperm development, cDNA and genomic MADS box clones have been isolated. The three cDNA clones ZEM1, ZEM2 and ZEM3 were cloned from a maize endosperm cDNA library using a probe based on sequences conserved in plant MADS box genes. Further transcripts were cloned by RT-PCR experiments and designated ZEM4 and ZEM5. Analysis of the corresponding genomic clones led to the identification of the ZEM2 MADS box gene family, three members of which were characterized sharing 97% sequence identity in corresponding domains. 100% sequence identities between cDNA and one of the genomic clones, conserved exon-intron boundaries and the demonstration of in vivo splicing in a maize endosperm transient expression system, show that the transcripts ZEM1-5 are derived by alternative splicing of ZEMa, one ZEM2 member. The ZEMa transcripts are present in almost all maize tissues, but specific differentially spliced forms accumulate preferentially in maturing endosperm and leaf. The function of the ZEMa gene is discussed in the light of similarities in the expression pattern with members of the human MEF2/RSRF gene family.